Expandable push-in orthopedic implant

ABSTRACT

A push-in orthopedic implant having an expandable height.

This application is a continuation of U.S. application Ser. No.10/011,652, filed Dec. 11, 2001, now U.S. Pat. No. 6,962,606; which is acontinuation of International Application No. PCT/US01/03657, with aninternational filing date of Feb. 5, 2001, published in English underPCT Article 21(2); which claims benefit of U.S. Provisional ApplicationNo. 60/180,404, filed Feb. 4, 2000; all of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an improved push-in interbody(for placement at least in part between adjacent vertebral bodies in thespace previously occupied by disc material) spinal fusion implant forthe immobilization of vertebrae. The present invention is directed toexpandable push-in implants only not including push-in implants havingsubstantially arcuate upper and lower members oriented toward theadjacent vertebral bodies and designed to engage the vertebral bodiesalong arcuate cuts therein typically formed by a drill. Further, thepresent invention is not directed to threaded implants requiringrotation for insertion into the implantation space in the spine. Inparticular, the invention relates to push-in spinal fusion implants thathave height raising capabilities that are utilized once the implant isinitially positioned. Such height raising capability may be utilizedwithin the spine anteriorly, posteriorly, or both and to variousextents, respectively so as to raise the front, back, or both of theimplant by the same or various amounts. More particularly, the inventionrelates to a push-in implant having upper and lower surfaces of upperand lower members that in a first or insertion position are collapsedrelative to one another and in a second or deployed position are adaptedto contact the adjacent vertebral bodies.

2. Description of the Related Art

Push-in spinal fusion implants having upper and lower surfaces adaptedfor placement in contact with adjacent vertebral bodies are known in therelated art. Such a push-in spinal fusion implant was invented byMichelson and is disclosed in U.S. Pat. No. 5,776,199, filed Jun. 28,1988, which is hereby incorporated by reference.

Lordotic or tapered, push-in spinal fusion implants are also known inthe art. By way of example, Michelson has invented such implants asdisclosed in U.S. Pat. No. 5,609,635, filed Jun. 7, 1995, which ishereby incorporated by reference.

Expandable fusion implants are known in the related art. The firstexpandable spinal fusion (allowing for the growth of bone from vertebralbody to vertebral body through the implant) implant was invented byMichelson and also is disclosed in U.S. Pat. No. 5,776,199 previouslyincorporated by reference herein.

Lordotic or tapered, spinal fusion implants have the advantage ofrestoring or enhancing spinal lordosis. Push-in spinal fusion implantsoffer the advantage of being easily positioned in the implantation spaceand of having excellent fastening or holding features. Expandable fusionimplants offer the advantage of allowing for the placement of apotentially larger implant through a smaller opening in a patient'sbody. Selective expansion along a single direction, (e.g. verticallyonly when correctly installed) offers the advantage of increasing theheight of the implant and therefore the distraction of the disc space,but without a concomitant increase in the width of the implant.

There exists a need for an artificial interbody spinal fusion implantproviding for all of the aforementioned advantages in combination.

SUMMARY OF THE INVENTION

In accordance with the present invention, as embodied and broadlydescribed herein, there is provided an expandable push-in artificialinterbody spinal fusion implant with upper and lower surfaces wheninserted, for insertion across a disc space between two adjacentvertebral bodies of a human spine. The push-in implant of the presentinvention includes an upper member having an upper surface adapted forplacement toward and into contact with one of the adjacent vertebralbodies and a lower member having a lower surface adapted for placementtoward and into contact with the other of the adjacent vertebral bodies.The upper and lower surfaces of the upper and lower members have atleast one opening in communication with one another for permitting forthe growth of bone from a vertebral body to an adjacent vertebral bodythrough the implant. The upper and lower members are articulatedtherebetween, preferably proximate one of the proximal ends and thedistal ends of the upper and lower members and preferably allow fordivergence between the articulating members at the end opposite thearticulating end of the implant. The upper and lower members have afirst position relative to one another that allows for a collapsedimplant height and a second position relative to one another that allowsfor an increased height. The upper and lower surfaces in the firstposition of the present invention of one embodiment are generally planarto one another.

As used herein the terms “generally or substantially planar” and“non-arcuate” are intended to describe the upper and lower surfaces ofthe implant of the present invention as having (1) no curvature, as in aplanar surface, (2) slight or mild curvature from the leading end to thetrailing end of the implant, and/or (3) slight or mild curvature acrossthe implant width. Slight or mild curvature does not include thecurvature associated with the upper and lower surfaces of implants forinsertion into a disc space having a circular cross section formedacross a spinal disc and into the adjacent vertebral bodies. While theupper and lower surfaces of the present invention may have somecurvature, in comparison to an implant having a circular cross section,the curvature is minimal. For implants having a circular cross sectionsuch as threaded implants the curvature of the upper and lower surfacescontacting the adjacent vertebral bodies is a radius of half the widthof the implant. If there is a curvature to the upper and lower surfacesof the present invention, the curvature is that of a circle much greaterthan the width of the implant; thus, it has a slight curvature that maycorrespond to an anatomical curvature of a disc or the surface of thevertebral endplate.

The upper and lower surfaces of the upper and lower members may beeither generally parallel or angled to one another when the implant isin the initial insertion position. In another embodiment, the upper andlower surfaces may have a relatively mild convexity in at least one orboth directions so as to better conform to the anatomical shape of thedisc space or the vertebral endplates. While a substantiallyparallelepiped shape having a quadrilateral cross section may begenerally preferred the leading and trailing ends may be substantiallyrounded to some advantage.

The height of the implant is at least that of the height of the restoreddisc space into which it is inserted. The implant is inserted at leastin part within the space that was previously occupied by the discmaterial that was contained between the vertebral bodies.

Preferably, on the exterior of each of the upper and lower surfaces isat least one bone-engaging projection adapted for linear insertion forengaging the adjacent vertebral bodies. The upper and lower members havea leading or distal end, an opposite trailing or proximal end, and alength therebetween. A blocker that is preferably in the form of anexpander is preferably located proximate at least one of the ends forholding at least a portion of the upper and lower members apart so as tomaintain the increased height of the implant and resist the collapse ofthe implant to the collapsed implant height. Expansion of the implantpreferably increases the implant height only, that is in a plane passingthrough the mid-longitudinal axis of the implant and the upper and lowermembers.

The blocker need not be in contact with the upper and lower members whenthe implant is initially inserted into the implantation space. Theblocker may be a block or any type of spacer that is inserted between orotherwise holds apart the articulated upper and lower members after theimplant is positioned so as to hold portions of the upper and lowermembers spaced apart the optimal height and angulation relative to oneanother. That is, the implant may be expanded with an extrinsic tool andthen the expanded portions held apart in the second position by a thirdbody blocker or blockers placed therebetween. Further, a physician maybe able to select from a series of blockers having different heightsusable with the same implant. The present invention includes expandingthe implant with a tool, such as a spreader or a distractor, but is notlimited to a scissors type, a rack and gear type, a threaded member typeor any other type of particular external expander tool mechanism. Eachtool nevertheless preferably engages the upper and the lower implantmembers to urge the implant apart. Then the blocker may be inserted intocontact with the upper and lower members to maintain the implant at anexpanded height. The height of the gap created by expanding the implantmay be measured so that the appropriately sized blocker or expander maybe inserted into contact with the upper and lower members depending uponthe amount of distraction of the implant desired by the physician.

In a preferred embodiment, the blocker is in contact with the upper andlower members prior to the implant expansion, and the blocker is itselfthe expander, which may be operated by an extrinsic tool. By way ofexample only, the expander may rotate: to increase the height of theimplant; in a single direction; more than 40 degrees and less than 140degrees and more preferably approximately 90 degrees to move from afirst insertion position to a second/deployed position; and in a planeperpendicular to the longitudinal axis of the implant to increase theheight of the implant. The expander preferably remains in the sameperpendicular plane relative to the longitudinal axis of the implantwhen rotated. In another embodiment the expander may be a member, suchas a plate, a rod, or of any other configuration suitable for theintended purpose initially within the interior between the upper andlower members in a collapsed position that is erected to a more erectposition when the implant is in the expanded position. The expander canbe hollow or solid.

In a preferred embodiment, the expander preferably has means including,but not limited to, an opening, a projection, or a detent adapted tocooperatively engage a tool used to rotate the expander to increase theheight of the implant. The opening, projection, or detent is adapted tocooperatively engage a tool that preferably rotates about an axisparallel to the longitudinal axis of the implant to rotate the expanderto increase the height of the implant. Rather then having an opening, aprojection, a detent, or a central aperture, the expander may have twoor more recesses or holes placed on or through the proximal face toengage a tool. In an alternative embodiment of the expander, cutouts maybe positioned along a portion of the perimeter of the expander.

The expander is preferably located proximate at least one of theproximal end or the distal end of the upper and lower members. Theexpander, however, need not be so located. The expander may be spacedaway from the end and even permit a hollow portion to exist on both theproximate and distal sides of the expander.

The upper and lower members preferably have an interior surfacetherebetween and a hollow defined therein with the expander locatedproximate one of the longitudinal ends of that interior hollow. Thehollow between the ends of the upper and lower members is preferablyunobstructed by the expander so as to permit growth of bone directlythrough the hollow unobstructed by the expander from vertebral body tovertebral body through the implant transverse to the longitudinal axisof the implant. The implant may comprise a second and lesser hollowextending at least in part from the expander to the end of the upper andlower members proximate that expander. A preferred expander mechanismincludes an expander in combination with cooperating surfaces of the endwall of the implant that guide and support the expander.

Preferred forms of interbody spinal fusion implants have a substantialhollow portion. Certain expandable interbody spinal fusion implants thatincrease in height only of the related art contain an expansionmechanism passing longitudinally therethrough or an expansion mechanismthat is configured for movement of the expansion mechanism fromproximate one end of the hollow portion to proximate the other end ofthe hollow portion, thus requiring the expander to pass through thelength of the hollow portion. A preferred embodiment of the presentinvention overcomes these limitations.

The expander moves the upper and lower surfaces relative to one anotherfrom a generally parallel or an angled orientation at a first positionto a generally parallel or an angled orientation at a second position orfrom a first height at each end to a second and greater height at atleast one and possibly both ends, including from a first height parallelorientation to a second height parallel orientation. In the firstposition for initial insertion, when used with an implant inserted fromthe anterior aspect of the spine the upper and lower surfaces arepreferably parallel or angled to be smaller at its leading end. Whenused with an implant inserted from the posterior aspect of the spine theupper and lower surfaces are preferably parallel or slightly angled tobe smaller at its leading end which is then reversed after it isexpanded. Each of the upper and lower members may structurally cooperatewith a blocker or expander so as to keep it located so as to functionfor its intended purpose. By way of example, each of the upper and lowermembers preferably has a track within which the blocker may be capturedor the expander rotated. The tracks may be configured to permit theexpander to rotate therein and then to move from side to sidetherewithin. The track of the upper member and the track of the lowermember are preferably in the same plane and the plane is preferablyperpendicular to the longitudinal axis of the implant.

A preferred expander has a first height in a first or insertion positionand a greater second height when rotated or positioned into a second ordeployed position to increase the maximum height of the implant from afirst maximum height to a second maximum height. By way of example, atleast one of the tracks of the upper and lower members preferably has acooperating surface and the expander has a corresponding cooperatingsurface that contacts the cooperating surface of the track to orient theexpander in a predetermined position. The cooperating surfacespreferably orient the expander within the implant such that the axis ofrotation of the expander is parallel with the longitudinal axis of theimplant and, more preferably, center the expander within the implantsuch that the axis of rotation of the expander coincides with thelongitudinal axis of the implant. As may be advantageous for the furtherloading of the implant with fusion-promoting material, the expander maycooperate with the tracking surfaces of the upper and lower members toallow the expander to slide from side-to-side for easier access to theimplant interior.

The implant is preferably packed with bone or other fusion-promotingsubstances prior to expansion of the implant. Expansion of the implantresults in a space being formed in the implant interior into whichadditional fusion promoting substances such as bone may preferably bepacked. Rotating the expander within the implant causes a void that canbe filled with bone. If the expander is configured to permitside-to-side movement, then packing of additional bone into the implantis facilitated.

When installing a preferred implant from the posterior approach to thespine, the implant is driven from the trailing end and the expander isat the leading end at the anterior aspect of the spine. When expanded,the implant installed from the posterior aspect leaves a void at theleading end of the implant near the anterior aspect of the spine becausethe leading end of the implant has been made taller, the void preferablybeing packed with bone. Additionally, the path left behind in the bonefilled interior of the implant by the tool used to access the expanderthrough the bone filled interior to position the expander is preferablypacked with bone as well.

In a preferred embodiment of the present invention, the expander heightchange from the first position to the second position corresponds tosubstantially the same change in height of the implant along at least aportion of the length of the implant. The expander may be configured indifferent ways. A preferred configuration for a rotational expanderincludes: a first dimension corresponding to the width of the expanderwhen the implant is initially inserted into the spine and to the heightof the rotational expander when the rotational expander is rotated toincrease the height of the implant; and a second dimension correspondingto the height of the expander when the implant is initially insertedinto the spine and to the width of the expander when the expander isrotated to increase the height of the implant. The first dimensionpreferably is greater than the second dimension.

The expander may have an upper surface, a lower surface, and sidesurfaces as defined when the expander is positioned after rotation toincrease the height of the implant. As used herein, the term “sidesurfaces” refers to those portions of the expander that extend from theupper member to the lower member after the expander has been rotatedinto its second or deployed position to increase the height of theimplant. The “upper” and “lower” expander surfaces refer to thoseportions of the expander that are in contact with the upper and lowermembers when the implant is in its second or expanded configuration.Each of the upper and lower surfaces of the expander may lie generallyin a plane and may be generally parallel to one another. The sidesurfaces and the upper and lower surfaces may be oriented so as tosubstantially form a parallelogram, which will typically be in the shapeof a rectangle generally.

A preferred expander is in the form of a modified rectangle or rhomboid.The expander generally has a longer dimension and a shorter dimension.When the expander is in a first position, the short dimension spans thedistance between the upper and lower members and when the expander is inthe second position, the expander's long dimension spans the distancebetween the upper and lower members.

The expander may have a cross-section with the side surfacesintersecting the upper and the lower surfaces at junctions, which may betwo diametrically opposed corners and two diametrically opposed arcs.The two diametrically opposed arcs may be each of the same radius and,preferably, the diagonal or modified hypotenuse “MH” between the opposedarcs has a maximum dimension that generally approximates the distancebetween the upper and lower surfaces such that, when the expander isrotated from a first insertion position toward a second/deployedposition, no substantial over-distraction occurs between the adjacentvertebral bodies as would occur if the height of the implant wasincreased markedly beyond that obtained in the second/deployed position.The two diametrically opposed corners may form a 90-degree angle. Theexpander preferably has a fixed shape during movement from a firstinsertion position to a second/deployed position within the implant.

In a preferred embodiment, a modified hypotenuse or diagonal “MH” is thedimension between the two diametrically opposed arcs that allows for therotation of the expander from a first position to a second positionwithout substantial over-distraction occurring during this process. Thephrase “without substantial over-distraction” is defined as distractingthe vertebral bodies in the range of elastic deformation and short ofplastic deformation and tissue failure. To avoid any ambiguity regardingthe phrase “without over-distraction,” this phrase and the individualwords contained therein are not being used as they may be in theirnormal or ordinary use, but are being used as defined in thisapplication only. In the example of this rotational expander, the MHcould be identical in length to the height thereby assuring literally nooverdistraction. It may be preferred, however, to have the MH justslightly greater in length than the height to insure the stability ofthe expander in the expanded or second position because this would thenrequire additional force over the stable position to derotate theexpander.

In accordance with an embodiment of the present invention, a secondexpander may be located between the upper and lower members for movingat least a portion of the upper and lower members away from one anotherto increase the height of the implant as defined by the maximum distancebetween the upper and lower surfaces proximate that expander. All of thefeatures described herein for the expander may also be applicable to thesecond expander. Additionally, the second expander may be locatedproximate an end of the implant opposite the other expander, therebyproviding an implant capable of being expanded at both ends of theimplant. The increased height of the implant resulting from moving thetwo expanders may be constant or varied along the length of the implantaccording to the desired configuration of the implant and the relativedimensions of the individual expanders. A given implant may be adaptedto receive or cooperatively engage a series of progressively sized(taller) blockers or expanders to allow the surgeon to make a finalheight selection at the time of surgery.

In accordance with an embodiment of the present invention, the implantmay include an expansion mechanism including the expander and at leastone partial wall structure preferably located proximate an implant endthat guides and holds the expander in a predetermined position.

The implant may have an overlapping step-cut wall junction between theupper and lower members, which offers as some of its advantages:increasing the lateral rigidity of the implant, holding the implant inthe closed first position until expanded, and to the extent desiredretaining the fusion-promoting materials within the implant. The walljunction may be either solid or perforated.

One of the upper and lower members preferably has an interior wallextending toward the other of the upper and lower members and, morepreferably, has two interior walls extending from each side of themember. The interior walls may be aligned parallel with the longitudinalaxis of the implant. The other one of the upper and lower memberspreferably has an interior-contacting surface adapted to contact orreceive the interior longitudinal wall.

By way of example, one of the upper and lower members may have alongitudinally extending interior wall, which is preferably unexposed,extending toward the other of the upper and lower members when theimplant is in an initial insertion position. When the implant is in thefinal expanded or deployed position the implant has a preferred shapesuch that each of the upper and lower surfaces of the upper and lowermembers are separated by at least a portion of interior wall, which inthis position preferably has an exposed side.

The upper and lower members in certain embodiments are articulated toone another so one of the respective ends of the upper and lower membersremain articulated while the other of the respective ends of the upperand lower members are free to move away from one another. In a preferredembodiment, the articulating is achieved without a third member, such asan axle shaft, for example, passing through the implant. Thearticulating structure preferably is formed into the implant wallsthemselves, and in a further preference in such a way that thetwo-implant halves may be articulated when at 90 degrees to each other.The halves then are moved, much like a book closing, toward each otherprior to insertion into the implantation space in the spine. Once theupper and lower members are closed from the approximately 90 degreesarticulating position, much like closing the leaves of a book, the upperand lower members of the implant are locked together at the articulationso that the members will not disarticulate when in use. Other types ofarticulation as would be known to one of ordinary skill in the art arewithin the scope of the present invention.

By way of example, the upper and lower members preferably have acooperating rotational articulation or pivot point between a proximateone of the proximal end and the distal end of the upper and lowermembers. The cooperating rotational articulation preferably is proximateone of the proximal end and the distal end of the upper and lowermembers at an end opposite the expander when only one end is to beexpanded. A preferred rotational articulation configuration includescooperating brackets and projections configured such that articulationtherebetween occurs when the upper and lower members are substantiallyperpendicular to one another. Such a configuration offers the advantagethat the brackets and the projections will not disengage one anotherwhen articulated for use such as insertion into the spine and subsequentexpansion within a range of movement of the upper and lower membersresulting from the expander positioning.

At least one and preferably both of the upper and lower members may havea screw hole passing through the trailing end, which preferably isadapted to receive a screw passing through the end of each of the upperand lower members and from the interior of the implant through the upperand lower surfaces, respectively, into each of the adjacent vertebralbodies to anchor the implant. The screw and implant combinationstabilize those vertebral bodies relative to each other, preventundesirable motion at the vertebral body implant interfaces, increasethe compressive load at the implant trailing end, prevent rocking; andthus mitigate against excessive peak loads and more uniformly distributeloads imparted to the implant over the length of the implant to theadjacent vertebral bodies.

The trailing end of the implant preferably has a tool-engaging portion,but the implant may be adapted to cooperatively engage a driver atanother location or by any means as would be known to one of ordinaryskill in the art. This tool-engaging portion is adapted to engage aninsertion tool that holds the implant during insertion into position inthe spine. The configuration of the tool-engaging portion may be anopening, and more particularly an opening that is along the longitudinalaxis of the implant. It is appreciated that the tool-engaging portionneed not be an opening. A hole or a blind hole, threaded or otherwise,is preferred in another embodiment. In another preferred embodiment theopening preferably is a threaded slot that functions to cooperativelyengage and disengage a tool for use in inserting the implant. Inspecific embodiments, the leading or trailing end may have wallportions, and/or be adapted to cooperatively engage a cap. Either theend wall portions or a cap may have an opening or openings that mayfunction to hold fusion-promoting materials within the implant and/or,permit vascular access and bone growth therethrough.

For an embodiment of an implant of the present invention having oneexpander, the main access opening is preferably at the end opposite fromthe expander. The main opening may be at either the distal or proximalend of the implant. The end of the upper and lower members containingthe expander may serve as a secondary access opening.

By way of example, an implant configured for insertion from an anteriorapproach may be initially packed from the distal or leading end of theimplant. The implant is then driven into position. Once the expander ismoved into final position and any associated tool for positioning theexpander is withdrawn from the expander, any void in the bone packedinto the implant interior may be filled. The expander may be moved fromside-to-side to pack more bone into the implant. In essence, theside-to-side movement of the expander provides for a secondary accessopening for accessing the hollow interior of the implant and forcompressively loading it with fusion-promoting substances.

The accompanying drawings, which are incorporated in and constitute apart of this specification, are by way of example only and notlimitation, and illustrate several embodiments of the invention, whichtogether with the description, serve to explain the principles of theinvention. The scope of the invention is limited only by the scope ofthe claims as from the present teachings other embodiments of thepresent invention shall be apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a spinal fusion implant of oneembodiment of the present invention;

FIG. 1A is a perspective view of an alternative embodiment of a blockerin the form of an expander for use with the spinal fusion implant ofFIG. 1;

FIG. 1B is a perspective view of another alternative embodiment of ablocker for use with the spinal fusion implant of FIG. 1;

FIG. 1C is a perspective view of yet another alternative embodiment of ablocker for use with the spinal fusion implant of FIG. 1;

FIG. 2 is a leading end plan view of the implant of FIG. 1;

FIG. 3 is a top view of the implant of FIG. 1;

FIG. 4 is a trailing end view of the implant of FIG. 1;

FIG. 5 is a side view of the implant of FIG. 1;

FIG. 6 is a cross-sectional side view along the mid-longitudinal axis ofthe implant of FIG. 1;

FIG. 7 is front view of one embodiment of an expander of the presentinvention;

FIG. 8 is a side elevation view of the expander of FIG. 7;

FIG. 9 is a schematic representation of a geometric configuration of across-section of an expander in accordance with one embodiment of thepresent invention;

FIG. 10 is a leading end perspective view of the implant of FIG. 1;

FIG. 11 is a side view of the implant of FIG. 1 being inserted from agenerally posterior approach to the spine into an implantation siteformed across a disc space and two adjacent vertebral bodies of thespine shown in partial cross-section;

FIG. 12 is a side view of the implant of FIG. 11 inserted in animplantation site formed across the disc space and two adjacentvertebral bodies of the spine;

FIG. 13 is a cross-sectional side view of the implant of FIG. 11 withthe implant in an expanded position inserted in an implantation siteformed across the disc space and two adjacent vertebral bodies of thespine;

FIG. 14 is a top view of two implants of FIG. 1 implanted in a finalposition upon the lower vertebral body of an implantation site formedposteriorly across a disc space;

FIG. 15 is a cross-section leading end view of the implant of FIG. 1implanted between adjacent vertebral bodies so as to show the expanderin the initial insertion position;

FIG. 16 is a cross-section leading end view of the implant of FIG. 1implanted between adjacent vertebral bodies so as to show the expanderin the final deployed position;

FIG. 17 is an exploded perspective view of a spinal fusion implant ofanother embodiment of the present invention;

FIG. 18 is a trailing end view of the implant of FIG. 17;

FIG. 19 is a top view of the implant of FIG. 17 with expander tracksshown in dashed lines;

FIG. 20 is a leading end view of the implant of FIG. 17;

FIG. 21 is a side view of the implant of FIG. 17;

FIG. 22 is a cross-sectional side view along the mid-longitudinal axisof the implant of FIG. 17;

FIG. 23A is a partial cross sectional view of an embodiment of aninterlocking wall design shown in the collapsed state for implants ofthe present invention;

FIG. 23B is a partial cross sectional view of an embodiment of theinterlocking wall design of FIG. 23A shown in a partially expandedposition for implants of the present invention;

FIG. 24 is a cross-sectional side view of an implantation site formedanteriorly across the disc space between two adjacent vertebral bodiesand the implant of FIG. 17 being installed into the implantation site;

FIG. 24A is a side view of an alternative implant having an anatomicallyshaped upper and lower surface for insertion from the anterior aspect ofthe spine;

FIG. 25 is a cross-sectional side view of the implantation site formedacross the space between two adjacent vertebral bodies and the implantof FIG. 17 installed into the implantation site;

FIG. 26 is a cross-sectional side view of the implantation site formedacross the space between two adjacent vertebral bodies and of theimplant of FIG. 17 installed into the implantation site in the finaldeployed position with upper and lower surfaces in angular orientationto one another and bone screws installed to anchor the implant;

FIG. 27 is a cross-sectional side view of the implantation site formedacross the space between two adjacent vertebral bodies and of theimplant of FIG. 17 installed into the implantation space in the finaldeployed position with upper and lower surfaces in parallel orientationto one another and bone screws installed to anchor the implant;

FIG. 28 is a top view the implant of FIG. 17 implanted in a finalposition upon the lower vertebral body of an implantation site formedanteriorly across a disc space with expander tracks shown in dashedlines and bone screws installed to anchor the implant;

FIG. 29 is a cross-sectional side view of an alternative embodiment ofan implant of the present invention with a pivoting trailing end that isalso a blocker with the trailing end in the open position;

FIG. 30 is a cross-sectional side view of an alternative embodiment ofan implant of FIG. 29 with the trailing end in the closed position;

FIG. 31 is a trailing end perspective view of the implant of FIG. 30

FIG. 32 is a partial fragmentary exploded front perspective view of anexpandable interbody spinal fusion implant with expanding and lockingend cap in accordance with a preferred embodiment of the presentinvention;

FIG. 32A is a rear perspective view of the end cap of FIG. 32;

FIG. 33 is a rear elevation view of the implant of FIG. 32;

FIG. 34 is a rear elevation view of the implant of FIG. 32 in anexpanded state and end cap inserted therein;

FIG. 35 is a side elevation view in partial cross section of the implantof FIG. 32 in an unexpanded state and end cap inserted therein;

FIG. 36 is a side elevation view in partial cross section of the implantof FIG. 32 in an expanded state and end cap inserted therein;

FIG. 37 is a fragmentary cross sectional side elevation view of theimplant of FIG. 32 in an expanded state showing a lip portion of theimplant trailing end against the outer perimeter of a recess in the endcap for preventing over-expansion of the implant;

FIG. 38 is a front perspective view of an expandable interbody spinalfusion implant with expanding and locking end cap in accordance withanother preferred embodiment of the present invention;

FIG. 39 is a rear elevation view of the implant of FIG. 38;

FIG. 40 is a side elevation view in partial cross section of the implantof FIG. 38 in an unexpanded state and end cap being inserted therein;

FIG. 41 is a side elevation view in partial cross section of the implantof FIG. 38 in an expanded state and end cap inserted therein;

FIG. 42 is a trailing end view of another preferred embodiment of theimplant of the present invention having four expanders and adapted to beinserted from an anterior approach to the spine;

FIG. 43 is a top plan view of the implant of FIG. 42 with bone screwsinstalled;

FIG. 44 is a leading end view of the implant of FIG. 42;

FIG. 45 is a side elevation view of the implant of FIG. 43;

FIG. 46 is a top plan view of the lower member of the implant of FIG.42;

FIG. 47 is a side view in partial cross section of a cap for use withthe implant of FIG. 42;

FIG. 48 is a top plan, view of a preferred embodiment of a bone screwfor use with the implant of FIG. 42;

FIG. 49 is a side elevation view of the screw of FIG. 48;

FIG. 50 is an exterior facing side elevation view of another preferredembodiment of an implant of the present invention adapted to be insertedfrom a posterior approach to the spine preferably in pairs;

FIG. 51 is a top plan view of the implant of FIG. 50;

FIG. 52 is a leading end view of the implant of FIG. 50;

FIG. 53 is a trailing end view of the implant of FIG. 50;

FIG. 54 is an interior facing side elevation view of the implant of FIG.50; and

FIG. 55 is a front elevation view of two disc levels of the lumbar spineshowing the prior art depth of resection resulting from drilling throughthe bony endplate region of adjacent vertebral bodies and showing theendplate region on a vertebral body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is intended to be representative only and notlimiting and many variations can be anticipated according to theseteachings, which are included within the scope of this inventiveteaching. Reference will now be made in detail to the preferredembodiments of this invention, examples of which are illustrated in theaccompanying drawings.

Human vertebral bodies have a hard outer shell of compacted densecancellous bone (sometimes referred to as the cortex) and a relativelysofter, inner mass of cancellous bone. Just below the cortex adjacentthe disc is a region of bone referred to herein as the “subchondralzone”. As best shown in FIG. 55, the outer shell of compact bone (thebony endplate) adjacent to the spinal disc and cartilaginous endplateand the underlying subchondral zone are together herein referred to asthe bony “end plate region” and, for the purposes of this application,is hereby so defined. In the lumber spine the bony endplate is generally2 mm deep. By way of example, prior art threaded implants requiringapproximately a 3 mm drill depth into the vertebral body will havethreads of approximately 1 mm or more resulting in a total depth ofpenetration into the vertebral body of 4 mm or more. The implant of thepresent invention and associated method permits the implant to penetrateinto the vertebral bodies to a depth of less than 3 mm or not topenetrate into the vertebral bodies.

Shown in FIGS. 1-6 and 10-16, in accordance with the present invention,as embodied and broadly described herein, is one embodiment of anexpandable push-in artificial interbody spinal fusion implant 100 forposterior insertion across a disc space D between two adjacent vertebralbodies V of a human spine. Push-in implant 100 of the present inventionincludes an upper member 102 having an upper surface 104 adapted forplacement toward and into contact with the upper of the adjacentvertebral bodies V and a lower member 106 having a lower surface 108adapted for placement toward and into contact with the lower of theadjacent vertebral bodies V. Upper and lower surfaces 104, 108 of upperand lower members 102, 106 have at least one opening 110, 112 incommunication with one another for permitting for the growth of bonefrom vertebral body V to adjacent vertebral body V through implant 100.Upper and lower members 102, 106 are articulated therebetween at anadjacent one of the proximal ends and the distal ends of upper and lowermembers 102, 106 and allow for rotation between the articulating membersat the end opposite the articulating end of implant 100. Upper and lowermembers 102, 106 have a first position relative to one another thatallows for a collapsed implant height and a second position relative toone another that allows for an increased height. Upper and lowersurfaces 104, 108 of upper and lower members 102, 106 in the firstposition of the present invention are parallel to one another. On anexterior 120 of each of opposed upper and lower surfaces 104, 108 ofupper and lower members 102, 106 is at least one bone-engagingprojection 118 adapted for linear insertion, which in one preferredembodiment is a ratchet. Alternatively, bone-engaging projection 118 canbe a surface roughening, knurling, or any other configuration suitablefor the intended purpose. While a specialized form of a blocker 121 isdescribed in significant detail below with reference to expander 122,blocker 121 need not be in contact with upper and lower members 102, 106when implant 100 is initially inserted into the implantation space.Blocker 121 may be a block or any type of spacer that is insertedbetween the articulated upper and lower members 102, 106 after implant100 is positioned so as to hold portions of the upper and lower members102, 106 spaced apart the optimal height and angulation relative to oneanother. That is the implant may be expanded with an extrinsic tool andthen the expanded portions held apart in the second position by a thirdbody blocker placed therebetween. Further, a physician may be able toselect from a series of blockers having different heights usable withthe same implant. The present invention includes expanding the implantwith a tool, such as a spreader or a distractor but is not limited to ascissors type, a rack and gear type, a threaded member type or any otherspecific type of movement mechanism. Each tool nevertheless preferablyengages upper and lower implant members 102, 106 to urge them apart.Blocker 121 is then inserted into contact with upper and lower members102, 106 to maintain implant 100 at an expanded height. The height ofthe gap created by expanding implant 100 may be measured so that theappropriately sized blocker 121 or specialized blocker, expander 122,may be inserted in implant 100 depending upon the amount of distractionof implant 100 desired by the surgeon.

Blocker 121 that is preferably in the form of expander 122 is locatedproximate at least one of the ends of the implant upper and lowermembers 102, 106 and holds at least a portion of upper and lower members102, 106 apart so as to maintain the increased height of implant 100 andresist the collapse of implant 100 to the collapsed implant height.Expander 122 in the present embodiment increases the implant height asmeasured in a plane passing through the mid-longitudinal axis of implant100 and upper and lower members 102, 106 during positioning of expander122 and as may be desirable is capable of selectively increasing theheight of the implant only.

Expander 122 in the present embodiment is adapted to rotate in a singledirection approximately 90 degrees to move from an initial (first)insertion position I, as best shown in FIGS. 1 and 10, to a final(second) deployed or expanded position F, as best shown in FIG. 16, toincrease the maximum height H of implant 100. Expander 122 preferablyrotates in a plane perpendicular to the longitudinal axis L of implant100 to increase the maximum height H of implant 100. During rotation,expander 122 remains in the same perpendicular plane relative to thelongitudinal axis L of the implant. It is appreciated that an expanderwithin the scope of the present invention may be designed to: rotate ineither direction or both directions; rotate more than 40 degrees andless than 140 degrees; rotate more or less than 90 degrees; or rotate ina plane other than perpendicular.

Expander 122 has an opening 124 adapted to cooperatively engage a tool(not shown) used to rotate expander 122 to increase height H of implant100. Opening 124 is adapted to cooperatively engage a tool thatpreferably rotates about an axis parallel to the longitudinal axis L ofimplant 100 to rotate expander 122 to increase height H of implant 100.Opening 124 also may be used as a passageway to pass fusion-promotingsubstances through expander 122 and into implant 100. It is appreciatedthat the expander may also include a projection, a detent, or any otherconfiguration in place of or in addition to an opening so as tocooperatively engage a tool to move the expander.

In an alternative embodiment, an expander 122′ could have cutouts alongany portion of its perimeter not involved in the actual rotation asshown in FIG. 1A. In another alternative embodiment, a blocker 121having cutouts along a portion of its perimeter can be positioned intothe implant as shown in FIG. 1B. The cutouts can be used to engage araised area within the implant to lock blocker 121 or expander 122′ intoposition or be used by the surgeon to grasp blocker 121 with a tool thatcooperatively engages the cutouts to facilitate inserting blocker 121into the implant. Rather then having an opening, a projection, a detent,or a central aperture, a blocker 121′ alternatively could have two ormore recesses or holes placed on or through the proximal face to engagea tool as shown in FIG. 1C.

As shown in FIGS. 1, 10 and 16, in one preferred embodiment of thepresent invention for posterior insertion, expander 122 is locatedproximate the leading end 150 of upper and lower members 102, 106. Inanother embodiment shown in FIGS. 17-28 for anterior insertion,expanders 222 used in implant 200 are located proximate each of thetrailing end 226 and leading end 250. An alternative embodiment of thepresent invention for anterior insertion shown in FIG. 29-31 has anexpander 322 located proximate trailing end 326 only of implant 300.Implant 100 preferably has an interior surface 128 and a hollow 130defined therein. Expander 122 of the present embodiment is locatedproximate interior surface 128 and more particularly proximate interiorsurface 128 at leading end 150 of upper and lower members 102, 106. Asis preferred, hollow 130 between the ends is unobstructed by expander122 so as to allow for the unimpeded loading of the interior of theimplant with the desired fusion-promoting substances; thus, loading theimplant is easy. Further, this preferred configuration of implant 100makes available all of the volume of the hollow to containfusion-promoting substances and so as to permit for the growth of bonedirectly through the hollow unobstructed by the expander to adjacentvertebral bodies V. Unobstructed hollow 130 further allows for packingimplant 100 with fusion-promoting substances. It is appreciated thatdepending on the intended results, the expander also may be located atdistal end 126 or leading end 150 of upper and lower members 102, 106 oranywhere else within the implant. The unobstructed hollow preferably hasno mechanism extending along the longitudinal axis of the implant whenfinally deployed and the mechanism that moves the implant from a firstposition to a second position preferably does not move expander 122longitudinally through the hollow portion. The expander may work bypivoting on a surface in contact with an interior wall portion of atleast one of the upper and lower members 102, 106. Moreover, multipleexpanders may be used in contact with upper and lower members 102, 106at any location within implant 100.

An alternative embodiment of an expander used with the present inventionincludes an expander having an external thread that cooperates withconverging threaded portions of the upper and lower members 102, 106 toexpand the implant as the expander is rotated into position. Anotheralternative embodiment of an expander includes an expander having a camconfiguration to expand the implant upon rotation.

The mechanism or tool used to move the expander is not part of theimplant itself as the mechanism or tool is removed from the implant uponmoving the expander, e.g. such as to rotate it into place and thusexpand the implant to the final expanded position.

Expander 122 of the present embodiment moves upper and lower surfaces104, 108 of upper and lower members 102, 106 from a parallel orientationP, as shown in FIGS. 11 and 12 where implant 100 is in a first position,to an angled orientation A, as shown in FIG. 13 where implant 100 is ina second position. It is appreciated that the expander also may move theupper and lower surfaces of the upper and lower members from a firstheight at each end to a second and greater height at each end.

FIG. 14 is a top view of two implants 100 implanted in a final positionupon a lower vertebral body of an implantation site formed posteriorlyacross a disc. In an alternative embodiment the corners of the trailingend may be chamfered, radiused, or otherwise relieved to ensure thatthey do not protrude beyond the vertebral bodies and the leading end maybe asymmetrical or otherwise shaped as may be beneficial for theintended purpose.

Similar implants may be used in the reverse direction, from anterior toposterior by moving the pivot to the leading end and having the expanderat the trailing end. Thus, the implant will get taller at its trailingend instead of its leading end. This smaller width implant design can beused to do an anterior approach spinal fusion where the surgeon wants toput in two implants instead of one large implant as when the surgery isto be preformed laproscopically.

In this embodiment, each of upper and lower members 102, 106structurally cooperate with expander 122 so as to keep it located so asto function for its intended purpose. Each of upper and lower members102, 106 of the implant of FIG. 1 has a track 132, 134 within whichexpander 122 rotates. As best shown in FIGS. 1 13, 15, and 16 track 132,134 is configured to permit expander 122 to rotate therein and then tomove from side to side within track 132, 134. Track 132 of upper member102 and track 134 of lower member 106 are in the same plane and theplane is perpendicular to the longitudinal axis of implant 100. It isappreciated that the track of the upper and lower members may be indifferent planes. Such a track design may be used with an expander witha step in it or with offset tabs to engage tracks in different planesthan one another. As with the expander, the tracks also may be atvarious angles to the longitudinal axis of the implant includingparallel with the longitudinal axis of the implant. Tracks 132, 134include sides 170 having cooperating surface 166 and expander 122 hascorresponding cooperating surface 168 used to orient expander 122 in apredetermined location. Cooperating surface 166 of side 170 is a detentand corresponding cooperating surface 168 of expander 122 is aprojection. The projection preferably projects toward expander 122 in adirection parallel to the longitudinal axis of implant 100. The detentand the projection preferably center expander 122 within implant 100such that the axis of rotation of expander 122 coincides with thelongitudinal axis of implant 100.

Other means for respectively engaging the implants and the expanderposition thereof are anticipated and within the scope of the presentinvention.

In rotating the expander, the longer dimension of the expander issubstituted for the lesser dimension of the expander thuscorrespondingly increasing the maximum height of the implant from thefirst to the second position. As best shown in FIG. 9, the schematicrepresentation of a geometric configuration of a cross-section of anexpander 122 in accordance with one embodiment of the present invention,includes: a first dimension X corresponding to the height of expander122 when implant 100 is initially inserted into the spine and to thewidth of expander 122 when expander 122 is rotated to increase height Hof implant 100; and a second dimension Y corresponding to the width ofexpander 122 when implant 100 is initially inserted into the spine andto the height of expander 122 when expander 122 is rotated to increaseheight H of implant 100. Second dimension Y is greater than firstdimension X. Expander 122 has an upper surface 136, a lower surface 138,and side surfaces 140 as defined when expander 122 is positioned afterrotation to increase height H of implant 100. As used herein, the term“side surfaces” refers to those portions of expander 122 that extendfrom upper member 102 to lower members 106 after expander 122 has beenrotated into its final deployed, or second position to increase theheight H of implant 100. The “upper” and “lower” surfaces refer to thoseportions of expander 122 that are in contact with upper and lowermembers 102, 106 when implant 100 is in its second position andconfiguration and is fully expanded.

A preferred expander 122 is in the form of a modified rectangle orrhomboid. The expander generally has a longer dimension Y and a shorterdimension X. When the expander is inserted into a first position, theshort dimension X spans the distance between upper member 102 to lowermember 106 and when expander 122 is in the second position, the longerdimension Y of expander 122 spans the distance between upper and lowermembers 102, 106.

Expander 122 in one embodiment of the present embodiment has across-section with side surfaces 140 intersecting upper and lowersurfaces 136, 138 at two junctions which may be diametrically opposedcorners 142 and two diametrically opposed arcs 144. Arcs 144 arepreferably each of the same radius and the modified hypotenuse MHbetween opposed arcs 144 generally approximates the distance betweenupper and lower surfaces 136, 138 such that, when expander 122 isrotated from an initial insertion position toward a final deployedposition, no substantial over-distraction occurs between adjacentvertebral bodies V. The modified hypotenuse MH of this embodiment of thepresent invention may be equal, slightly less than, or slightly greaterthan dimension Y of expander 122. Having the modified hypotenuse MH beslightly greater than the dimension Y offers the advantage of havingexpander 122 stabilized by an over-center position, such that moreenergy would be required to derotate the expander than for it to remainin the deployed or second position. By “without substantialover-distraction” what is meant is that the modified hypotenuse MHlength is closer to the expander dimension Y than to the unmodifiedhypotenuse UH; and is selected to allow the implant to preferablyoperate in the range of elastic deformation of the tissues about theoperated disc space. Corners 142 may form, but not necessarily, a90-degree angle and have an unmodified hypotenuse dimension UH.

By way of example, consider one embodiment of expandable implant 100 ofthe present invention having an optimum expanded height of 18 mm for agiven implantation space. Any implant bigger than 18 mm should not beused in this implantation space because during expansion of the implant,its height would move through the range of elastic deformation of thesurrounding tissues and after that the implant would crush the vertebralbone or tear ligaments. Inserting an expander such that when the implantis fully expanded allows the implant to be 18 mm would be ideal. It maybe that an implant having a 17.5 mm expanded height for thisimplantation space is nearly as good, but a 16 mm expanded height may betoo short to fit tightly within the implantation space. Using apreferred rectangular expander without any modification to thehypotenuse that is adapted to expand the implant to the optimum 18 mmfinal height would require the expander to have a hypotenuse causing theimplant to exceed the 18 mm expanded height temporarily during rotationof the expander. So turning the expander without a modified hypotenusewould break the vertebrae or tear the ligaments. In reverse, if onecould not expand the implant to more than 18 mm without causing damageto the spine, then an implant selected to have an expander having a fullunmodified hypotenuse so as to upon rotation temporarily cause theimplant height to be 18 mm would in the finally expanded position allowthe implant height to collapse such that there would be insufficientheight for the implant to adequately distract the implantation space.Generally, the modified hypotenuse of the expander is closer in lengthto dimension Y of the expander than to the unmodified hypotenuse.

As best shown in FIG. 1 in this particular embodiment, expander 122 hasa depth dimension Z that is less than that of first and seconddimensions Y, X. Expander 122 of the present embodiment has a fixedshape during movement from initial insertion position I to finaldeployed position F within implant 100.

While modified hypotenuse MH is illustrated as being between arcs 144 inthis preferred embodiment, the configuration of expander 122 to formmodified hypotenuse MH can take many forms, such that those junctionsare relieved so as to have the desired lesser dimension therebetween,including arcs, chamfers, a series of angled surfaces, or any othershape so long as the modified hypotenuse MH is sufficiently reduced indimension to function for the intended purpose according to the presentteaching.

An embodiment of the present invention where modified hypotenuse MH isslightly greater than height Y offers the advantage of an over-centereffect that locks expander 122 into place. In this instance, onceexpander 122 rotates past the diagonal of the modified hypotenuse MH,more force would be required to rotate it back from the final deployedposition to its insertion position than in an embodiment where modifiedhypotenuse MH is equal to or less than height Y. Preferably, expander122 offers a surgeon multiple sensory advantages including: the tactilefeel of expander 122 going over center and locking into place; thevisual of the handle of a tool rotating expander 122 such that the toolhandle goes from perpendicular to parallel, the reverse, or other, tothe disc space into place; and auditory from the sound of expander 122snapping into place.

Each of upper and lower surfaces 136, 138 of expander 122 of the presentembodiment lie generally in a plane and are generally parallel to oneanother. For any implant it is anticipated that a physician may be ableto select from a series of blockers or expanders allowing for varyingthe increase in the implant height. Side surfaces 140 and upper andlower surfaces 136, 138 are oriented so as to substantially form aparallelogram. Any of a number of configurations for the expander forincreasing the height of the implant is possible, based on the teachingsof the present application and such configurations as would be known toone of skill in the art are anticipated within the scope of the presentinvention.

The implant may preferably have an overlapping step-cut wall junctionbetween upper and power members 102, 106 which offers the advantage ofincreasing the lateral rigidity of implant 100 holding the implant inthe closed first position until expanded, and to the extent desiredretaining the fusion-promoting materials within. The wall junction maybe either solid or perforated. As best shown in FIG. 1, upper member 102in one embodiment of the preferred invention has interior walls 146extending from each side of upper surface 104 toward lower member 106.Interior wall 146 is aligned parallel to longitudinal axis L of implant100. Lower member 106 has an interior-contacting surface 148 adapted tocontact or receive interior wall 146.

In a preferred embodiment, upper and lower members 102, 106 arearticulated to one another so one of the respective ends of upper andlower members 102, 106 remain articulated while the other of therespective ends of upper and lower members 102, 106 are free to moveaway from one another. In a preferred embodiment the articulating meansis achieved without a third member such as an axle shaft passing throughthe implant. The articulating means preferably is formed into theimplant walls themselves in such a way that the two implant halves maybe articulated when the halves are at 90 degrees to each other and thenthe halves are moved toward each other for insertion into theimplantation space in the spine. The two halves are closed much like thecover of a book. The halves are locked together such thatdisarticulation will not occur when the implant is assembled for use.Any of a number of ways of articulating or joining upper and lowermembers 102, 106 is possible.

As best shown in FIG. 1 in this embodiment, upper and lower members 102,106 of the present embodiment have a pivot point between adjacent distalends 126 of upper and lower members 102, 106. The pivot point in thepresent embodiment is at the end of implant 100 opposite expander 122.The pivot point of the present embodiment operates as a hinge or axle152 but is formed out of the walls themselves so as to preferably notintrude into the implant interior or hollow or to block access thereto.Hinge 152 includes a projection 154 extending radially from each side ofinterior-contacting surface 148 of lower member 106 and a slottedbracket 156 extending from each side of upper member 102 for engagingprojection 154. Brackets 156 and projections 154 are configured suchthat engagement occurs when upper and lower members 102, 106 aresubstantially perpendicular to one another. Brackets 156 and projections154 are configured so as not to disengage within a range of movement ofupper and lower members 102, 106 that would occur when the implant is inuse either during insertion or resulting from the expansion in height ofimplant 100.

As best shown in FIGS. 10-12 and 15, interior-contacting surface 148 oflower member 108 of the present embodiment is unexposed when implant 100is in initial insertion position I. As shown in FIG. 16, when implant100 is in the expanded position F, implant 100 has a shape such thateach of upper and lower members 102, 106 are separated by at least aportion of interior-contacting surface 148, which in this position hasan exposed side. The exposed side of the present embodiment is smoothand flat.

A slot 158 on implant 100 is adapted to receive in a lockable way adriver and to thereafter, if so desired by the surgeon, a cap that snapsinto slot 158. As discussed above, implant 100 has a leading end 150 anda trailing end 126. One of the ends preferably has a tool-engagingportion. This tool-engaging portion is adapted to engage an insertiontool that holds implant 100 during insertion into position into thespine. The tool-engaging configuration may be an opening, and moreparticularly an opening that is along the longitudinal axis of theimplant. Of course, the tool-engaging portion need not be an opening. Ahole or a blind hole, threaded or otherwise, is preferred in anotherembodiment. In another preferred embodiment the opening preferably is athreaded slot that functions to cooperatively engage and disengage atool for use in inserting implant 100.

A cap having an exterior surface and an interior surface may be used toclose trailing end 126 of implant 100. The interior surface of the capmay have spaced slots about its circumference to facilitate a snap fitbetween the cap and the implant 100. The cap and implant 100 can ofcourse be adapted for either or both ends of implant 100. Further, thecap may be solid or perforate and made of a surgical quality plasticthat may be resorbable or of any other suitable material.

For a posterior approach implant, it may be desirable to have a cap onthe trailing end. The trailing end of the implant in a posteriorapproach implant has direct exposure to the spinal canal where thespinal cord and nerve roots are located. A cap on a posterior approachimplant may be for the purpose of sealing off the spinal canal from thefusion-promoting substances contained in the hollow interior of theimplant so that no bone grows into the canal. Further, the presentinvention implant may be used in combination with chemical substancesand/or compounds applied at the trailing end of the implant to inhibitscar formation, and the cap may be of benefit in shielding thefusion-promoting substances contained in the implant from these scarformation inhibiting chemicals and compounds. It may also be for thepurposes identified herein used in association with the leading end capof an anterior approach implant. An anterior approach implant may have aleading end, trailing end, or both ends that are adapted to engage acap. One of the purposes for that cap includes restricting the passageof fusion-promoting substances so that they remain loaded within theimplant. Another purpose of the cap may be to add structural support tothe implant. The cap may be solid or it may have openings therethrough.Any such openings could allow for the loaded material to stay within theimplant while providing for vascular access to allow for the ingrowth ofblood vessels and the growth of bone through the end of the implant.

Shown in FIGS. 17-28, in accordance with the present invention, asembodied and broadly described herein, is an embodiment of an expandablepush-in artificial interbody spinal fusion implant 200 for anteriorinsertion across a disc space D between two adjacent vertebral bodies Vof a human spine. Push-in implant 200 of the present invention includesan upper member 202 having an upper surface 204 adapted for placementtoward and in contact with the upper of the adjacent vertebral bodies Vand a lower member 206 having a lower surface 208 adapted for placementtoward and in contact with the lower of the adjacent vertebral bodies V.Implant 200 in FIGS. 24 through 28 is shown being implanted into thespine from the anterior aspect with expanders 222 on the distal end 226and leading end 250 of implant 200. While anterior and posterior aspectapproaches have been illustrated herein, the present invention is notlimited to these illustrated approaches. In particular, but not limitedthereto, the push-in implant of the present invention also may be usedin push-in implants for insertion from the translateral aspect of thespine as disclosed by Michelson in U.S. Pat. No. 5,860,973, which isincorporated herein by reference.

FIG. 24A is a side view of an alternative implant having an anatomicallyshaped upper and lower surface for insertion from the anterior aspect ofthe spine. The anatomical curvature may correspond to that of a disc orthe surface of the vertebral endplate. In another embodiment, the upperand lower surfaces may have a relatively mild convexity in bothdirections, that is from leading to trailing end as well as side-to-sideso as to better conform to the anatomical shape of the disc space or thevertebral endplates.

In accordance with this embodiment of the present invention, a secondexpander 222 is located at least in part between upper and lower members202, 206 for moving at least a portion of the upper and lower membersaway from one another to increase the height of implant 200 defined bythe maximum distance between upper and lower surfaces 104, 108 of upperand lower members 202, 206. All of the features described herein for thesingle expander 122 of implant 100 of FIGS. 1-16 may also be applicableto both expanders 222 of implant 200. Additionally, second expander 222may be located proximate an end of implant 200 opposite other expander222, thereby providing implant 200 the capability of being expanded atboth ends 226, 250 of implant 200. The increased height of implant 200resulting from moving two expanders 222 may be the constant or variedalong the length of implant 200 according to the desired configurationof implant 200. FIGS. 25 and 26 show expanders 222 moving upper andlower surfaces 204, 208 from a parallel orientation to an angledorientation relative to one another. FIGS. 25 and 27 show alternativeexpanders 222 moving upper and lower surfaces 204, 208 from a firstheight parallel orientation to a second height parallel orientation. Inboth events upper and lower surfaces 204, 208 in the first or insertionposition are parallel to one another over a substantial portion of thelength of the implant.

As best shown in FIG. 17, tracks 232, 234 of upper and lower members202, 206 of the second embodiment have a cooperating surface andexpanders 222 have a corresponding cooperating surface that contacts thecooperating surface of tracks 232, 234 to orient expanders 222 in apredetermined location. The cooperating surfaces orient expanders 222within implant 200 such that the axis of rotation of expanders 222 areparallel to the longitudinal axis of implant 200 and more particularlycenter expanders 222 within implant 200 such that the axis of rotationof expanders 222 coincide with longitudinal axis L of implant 200.

As best shown in FIGS. 25-28, another aspect of implant 200 is that itsupper and lower members 202, 206 have screw holes 274 passingtherethrough adapted to receive a screw 278 passing from the interior ofimplant 200 into adjacent vertebral bodies V to anchor implant 200 to anadjacent vertebral body V.

The articulation may be of one of two general types, examples of whichare each herein disclosed. As shown in previously described embodimentsof the present invention, the articulation may allow rotation about thearticulation. A second type of articulation allows for both rotation andexpansion at the point of articulation. An example of this is shown inFIGS. 17 and 21, where a peg and hook design is utilized. In thisexample both functions, that is, rotation or pivoting, and captured orlimited expansion with a fixed end point or stop, occur at the samelocation. Alternatively, and without departing from the teachings of thepresent invention, those functions can be divided. By way of exampleonly, and not limitation, expansion can be allowed and controlled by aninterlocking wall design, as shown by the interlocking members in thealternative embodiments of FIGS. 23A and 23B. FIG. 23A is a partialcross sectional view of an embodiment of an interlocking wall designshown in the collapsed state for implants of the present invention. FIG.23B is a partial cross sectional view of an embodiment of theinterlocking wall design of FIG. 23A shown in a partially expandedposition for implants of the present invention. Various other structuralfeatures as would be obvious to one of ordinary skill in the art afterthe teachings herein can similarly be employed.

A fixed end point for the implant expansion is preferred for the properfunctioning of the opposed bone screws. A purpose of the opposed bonescrews is to rigidly secure the implant within the vertebral segment. Afurther purpose is to pull each of the adjacent vertebral bodies towardthe implant and towards each other so as to have a construct resistantto the deleterious effects of vertebral rocking as may otherwise occurwith spinal flexion and extension absent such restraint. If thearticulation device captures the upper and lower members together, as inthe embodiment of posterior implant 100 of FIGS. 1-16, by closelyencircling a post then the implant cannot expand at that location. Sothe coupling mechanism of FIGS. 17 and 21 permit the upper and lowermembers to remain articulated, permit the implant to expand, and permitthe screws to pull against the implant and each other, in oppositedirections and to pull the bones toward each other. An optional extendedslot and peg configuration may be added toward leading end 250 ofimplant 200, however, this is not needed to hold the implant together.

An alternative embodiment of an implant for use from the anteriorapproach is shown in FIGS. 29 through 31. In implant 300 blocker 322takes the form of a trailing wall that articulates or hinges to theinside of implant 300. The trailing wall may be left open duringinsertion of implant 300 so as to trail behind the upper and lowermembers. Once implant 300 is implanted into position, the trailing wallis rotated about one of its ends and pushed into position and lockedinto place. This may occur by having the trailing wall contact aninclined plane that leads up to a notch into which the trailing walllocks into place. The trailing wall itself may also have at least oneopening in it to permit the further loading of fusion-promotingmaterials into implant 300. Blocker 322 may also be adapted tocooperatively engage a tool used to move the blocker from an initialposition to a final position to increase the height of implant 300, thetool being removable after moving blocker 322 into the final position.

Implant 300 may be configured to have a rotational articulation betweenthe upper and lower members adjacent one of the ends of the upper andlower members. The rotational articulation may be formed by the upperand lower members interdigitating so as to cooperatively engage. Therotational articulation may be configured so that engagement occurs whenthe upper and lower members are substantially perpendicular to oneanother. The rotational articulation may also be configured to remainengaged within a ramie of movement of the upper and lower membersresulting from positioning implant 300 between a first position of theupper and lower members relative to one another allowing for a collapsedimplant height and a second position relative to one another allowingfor an increased implant height.

At least one or both of the upper and lower members of implant 300 maybe configured to have a screw hole passing therethrough that is adaptedto receive a screw passing from an interior of implant 300 into anadjacent vertebral body. The screw may be adapted to pass from theinterior of implant 300 through the screw hole and into the adjacentvertebral body to anchor implant 300 to the adjacent vertebral body.

Implant 300 may be configured to have a side surface contoured tocooperate with another implant when implant 300 is in a final position.Implant 300 and the cooperating implant may have a combined widththerebetween less than the combined height of implant 300 and thecooperating implant.

FIGS. 32-37 show a preferred embodiment of an expandable interbodyspinal fusion implant 400 and an expanding and locking end cap 500 foruse therewith in accordance with the present invention. As shown inFIGS. 32 and 33, implant 400 preferably has a trailing end 426 thatincludes openings 480 to permit for the growth of bone through implant400. Implant 400 has a bone-engaging projection that is preferably oneof ratchets, splines, knurling, or other surfaces roughenings to resistexpulsion of the implant from the disc space after implantation.

As shown in FIGS. 35 and 36, by way of example, upper and lower members402, 406 preferably have upper and lower screw holes 474 passingtherethrough, each adapted to receive a bone screw 478 passing from theinterior of implant 400 into an adjacent vertebral body to anchorimplant 400 to an adjacent vertebral body. Bone screws are not essentialto the operation of the invention, but are preferable for providingadded securement of the implant to the adjacent vertebral bodies.

In certain circumstances, upper and lower members 402, 406 can move awayfrom one another and merely securing upper and lower members 402, 406 tothe adjacent vertebral bodies with bone screws is not adequate. Anexample of such a circumstance occurs when the surgeon elects toapproach the spine anteriorly, which generally requires severing and/orremoving substantial portions of the anterior longitudinal ligament overthe operated area. The anterior longitudinal ligament is positionedalong the anterior spinal surface and prevents hyperextension of thespine as an individual bends backward. Because the anterior longitudinalligament covers the anterior spinal surface, the surgeon must cutthrough this tough ligament to access the disc space below, compromisingthe stability of the spine. Specifically, the anterior longitudinalligament is generally lax, except when an individual leans backward,then the ligament acts as a tension band resisting elongation. If theanterior longitudinal ligament is damaged, there is no check on thatspinal movement and the vertebral bodies may detrimentally angulate.Thus, a mechanism is needed to prevent movement of the upper and lowermembers relative to one another beyond a predetermined amount.

FIGS. 32-33 show expanding and locking end cap 500 for use with implant400. The end cap is capable of one or more of the following functions:(1) expands the implant by moving the upper and lower members apart, (2)maintains the implant in an expanded state by holding at least a portionof the upper and lower members apart so as to maintain the increasedheight of the implant and resist the collapse of the implant to thecollapsed implant height, (3) prevents the implant from expanding beyonda predetermined amount by engaging at least a portion of the upper andlower members, and (4) locks bone screws to the implant by blocking theexit path of the bone screws in a direction opposite to the direction ofinsertion. Expansion of the implant preferably increases the implantheight only, that is in a plane passing through the mid-longitudinalaxis of the implant and the upper and lower members. In a preferredembodiment, the end cap is capable of performing all four of theaforementioned functions.

As shown in FIGS. 32 and 33, trailing end 426 of implant 400 preferablyhas an opening 482 adapted to engage cap 500 and may also provide accessto the interior of implant 400 for the purpose of introducing bonegrowth promoting materials therein. Upper and lower interior surfaces484, 486 of opening 482 preferably have a portion that extends beyondexterior trailing end surface 488, forming upper lip portions 490 andlower lip portions 492, respectively. When implant 400 is in anunexpanded state, the profile of upper and lower lip portions 490, 492preferably form the shape of at least a portion of an oval. In theexpanded state of implant 400, the profile of upper and lower lipportions 490, 492 preferably becomes less oval and generally morecircular in shape. For example, upper and lower lip portions 490, 492can be arcs of a circle such that in the expanded state, the arcs wouldbe part of the same circle.

Cap 500 has a head 502 and a stem 504. Head 502 has a perimeterpreferably sized and shaped to cover at least a portion of upper andlower bone screw holes 474 so as to lock bone screws 478 to implant 400.Head 502 has a top surface 506, a bottom surface 508, and a rim 510. Topsurface 506 has a tool engagement area 512 that is preferably adapted tocooperatively engage an insertion tool. Tool engagement area 512preferably includes a hex-shaped recess 514 and a groove 516 adapted toengage correspondingly-shaped tools, respectively. Other shapes arepossible for tool engagement area 512 depending upon the type ofinsertion tool used with the present invention, all of which are withinthe broad scope of the present invention.

Top surface 506 of cap 500 preferably has a bevel 518 extending aroundthe perimeter thereof to form a reduced profile. Top surface 506 mayhave any shape suitable for its intended purpose and it is preferablethat such shape does not extend from trailing end 426 so as not tosubstantially interfere with delicate vascular and neurologicalstructures adjacent thereto after implant 400 is installed in the spine.

As shown in FIG. 32A, bottom surface 508 of cap 500 has a recess 520proximate the perimeter of bottom surface 508 that is adapted tointeract with upper and lower lip portions 490, 492 of implant 400. Asdescribed in further detail below, the interaction of lip portions 490,492 and recess 520 limits the over-expansion of implant 400. Recess 520has an inner perimeter 522, an outer perimeter 524, and a widththerebetween adapted to accommodate the profiles of at least a portionof upper and lower lips 490, 492 of implant 400 in both an unexpandedand expanded state. The surface of outer perimeter 524 forms a flangethat acts as a stop against which upper and lower lip portions 490, 492of implant 400 are prevented from further movement away from themid-longitudinal axis of implant 400 when implant 400 and cap 500 areengaged, as will be described in more detail below.

Stem 504 of cap 500 projects from bottom surface 508 and is sized andshaped to cooperatively engage opening 482 in trailing end 426 to expandimplant 400 and to maintain implant 400 in an expanded state. Stem 504preferably has a distal end 526 with tabs 528, 530, an upper surface532, a lower surface 534 opposite to upper surface 532, and sides 536,538. Tabs 528, 530 are configured to engage the interior surface oftrailing end 126 such that when properly positioned within opening 482,tabs 528, 530 prevent cap 500 from backing out of opening 482 of implant400.

Sides 536, 538 of stem 504 are configured to cooperatively engage upperand lower interior surfaces 484, 486 of opening 482. Opening 482 mayhave any shape suitable for its intended purpose for interacting withstem 504. For example, sides 536, 538 may be beveled or rounded toaccommodate rotational contact with upper and lower interior surfaces484, 486. Stem 504 may have a generally rectangular cross-section or mayhave a cross-section with sides 536, 538 intersecting the upper and thelower surfaces 532, 534 at junctions, which may be two diametricallyopposed corners and two diametrically opposed arcs. The twodiametrically opposed arcs may be each of the same radius and,preferably, the diagonal or modified hypotenuse “MH” between the opposedarcs has a maximum dimension that generally approximates the distancebetween the upper and lower surfaces 532, 534 such that, when stem 504is rotated from a first insertion position toward a second/deployedposition, no substantial over-distraction occurs between the adjacentvertebral bodies as would occur if the height of the implant wasincreased markedly beyond that obtained in the second/deployed position.The two diametrically opposed corners may form a 90-degree angle.Additionally, sides 536, 538 may be configured to be divergent away fromdistal end 526 to better accommodate engagement with upper and lowerinterior surfaces 484, 486 while implant 400 is in the expanded state.

FIGS. 34-36 show a preferred expansion of implant 400 by cap 500. InFIG. 35, stem 504 of cap 500 is inserted through opening 482 in trailingend 426 of implant 400. After stem 504 is inserted into opening 482,tabs 528, 530 extend beyond upper and lower interior surfaces 484, 486of opening 482 and into the interior of implant 400. Upper and lowersurfaces 532, 534 of stem 504 are oriented toward upper and lowerinterior surfaces 484, 486 of opening 482, respectively, such thatimplant 400 is in a collapsed state. As cap 500 is rotated 90° in eitherdirection, sides 536, 538 of stem 504 cooperatively engage with upperand lower interior surfaces 484, 486 of opening 482, forcing apart upperand lower members 402, 406 away from the mid-longitudinal axis ofimplant 400 to position implant 400 in an expanded state. The rotationof cap 500 moves upper and lower members 402, 406 from a generallyparallel orientation shown in FIG. 35 to an angled orientation shown inFIG. 36. During expansion of implant 400, upper and lower lip portions490, 492 move within recess 520 of cap 500 until stem 504 ceases movingupper and lower interior surfaces 484, 486 away from themid-longitudinal axis of implant 400.

FIG. 37 shows a partial cross-section along line 37-37 of FIG. 34. Asshown in FIG. 37, the maximum expansion of upper member 402 is reachedwhen upper lip portions 490 are blocked from further motion away fromthe mid-longitudinal axis of implant 400 upon reaching outer perimeter524 of recess 520. Although not shown in FIG. 37, lower lip portions 492similarly contact outer perimeter 524 of recess 520. In this manner, theexpansion of implant 400 beyond a predetermined amount is prevented.Tabs 528, 530 of stem 504 bear against the interior of implant 400 andprevent removal of end cap 500 from opening 482. In the deployedposition, end cap 500 locks implant 400 in an expanded state.

As shown in FIGS. 38-41, another preferred embodiment of the implant andend cap of the present invention is shown and generally referred to bythe reference numbers 600 and 700, respectively. Implant 600 is similarto implant 400, except that opening 682 of implant trailing end 626preferably has at least one thread 694 for cooperatively engaging with athreaded stem 704 of cap 700.

Cap 700 is similar to cap 500, except for differences noted below. Head702 includes an upper cutout portion 740 and a lower cutout portion 742,each being adapted to allow the passage of a bone screw 678 into implant600 after cap 700 has been attached to implant 600. Once bone screws 678are inserted, cap 700 may be rotated such that at least a portion ofhead 702 covers each of screws 678. Upper and lower cutout portions 740,742 allow the surgeon the option of inserting bone screws 678 before orafter attachment of cap 700 with implant 600.

Stem 704 has at least one thread 748 along the mid-longitudinal axis ofcap 700 for cooperatively engaging with threaded opening 682 of implant600. Distal end 726 of stem 704 has an upper surface 744 and a lowersurface 746 that are convergent towards distal end 726 for assisting inthe insertion of stem 704 into opening 682 of implant 600.

As shown in FIGS. 40 and 41, cap 700 is inserted into trailing end 626of implant 600, preferably by aligning the edge of distal end 726 withthe plane separating upper and lower members 602, 606. Once upper andlower surfaces 744, 746 of distal end 726 are sufficiently withinthreaded opening 682 of implant trailing end 626, cap 700 is rotated toallow stem thread 748 of cap 700 to cooperatively engage with threadedopening 682. The engagement of stem thread 748 with threaded opening 682spreads apart upper and lower members 602, 606 at least along a portionof the length of implant 600. Continued rotation of cap 700 forces upperand lower lip portions 690, 692 to contact recess 720 of cap 700. Thepitch of thread 748 is preferably such that as upper and lower lipportions 690, 692 reach recess 720, they come into contact with at leasta portion of the outer perimeter of recess 720. Upon contact with recess720, upper and lower lip portions 690, 692 are prevented from furthermovement away from the mid-longitudinal axis of implant 600.

Those skilled in the art will appreciate that although it is preferredto use a cap to prevent over-expansion of an expandable implant, theinvention is not so limited. For example, the implant trailing end maybe adapted to have lip portions along the trailing end interior surfacefor cooperatively engaging with a recess and/or flange to preventover-expansion of the implant. In such an instance, an over-expansioninhibiting surface may operate without a stem and/or head by relying onadditional surface features of the implant trailing end, for example, akey-way entry along the opening leading to the interior lip portions ora circumferential barrier beyond the interior lip portions forpreventing the over-expansion surface from traveling too far into theimplant interior. Although the expander implant cap has been describedwith respect to a threaded expanding spinal fusion implant, it may beadapted for use with any expandable spinal implants including any of thevarious implant embodiments disclosed herein.

FIGS. 42-46 show another preferred embodiment of the implant 800 that isadapted to be inserted from an anterior approach to the spine. Inimplant 800 two sets of expanders 822 are used, each set being locatedon one side of the mid-longitudinal axis of implant 800. Depending uponthe type of articulation used, expanders 822 may be rotated to confer atransverse angulation as well as longitudinal angulation to the upperand lower members of implant 800 in situations where such angulation isdesired. All four expanders 822 may be used to expand the upper andlower members of implant 800 by the same or different amount relative toone another. This can be done to permit the surgeon to expand theleading and trailing ends or sides by varying degrees.

Another aspect of implant 800 is that its upper and lower members havescrew holes passing therethrough adapted to receive a bone screw passingfrom the interior of implant 800 into adjacent vertebral bodies toanchor implant 800 to an adjacent vertebral body. A purpose of theopposed bone screws is to rigidly secure the implant within thevertebral segment. A further purpose is to pull each of the adjacentvertebral bodies toward the implant and towards each other.

FIG. 47 shows a preferred embodiment of an end cap 898 for locking thebone screws to implant 800. The end cap is preferably configured tothreadably engage the opening in the trailing end of implant 800.

FIGS. 48 and 49 show a preferred embodiment of a bone screw 900 for usewith implant 800. Bone screw 900 preferably has a threaded head portionto threadably engage the screw holes of implant 800. Bone screw 900 isself-locking since the thread pattern of the head is different from thethread pattern along the shaft of the screw that penetrates the bone. Itis appreciated that bone screws are not essential to the operation ofthe invention, but are preferable for providing added securement of theimplant to the adjacent vertebral bodies.

FIGS. 50-54 show another preferred embodiment of an implant 1000 of thepresent invention adapted to be inserted from a posterior approach tothe spine. Implant 1000 is preferably installed in pairs, to either sideof the mid-sagittal axis of the vertebral bodies. Each implant 1000 inthe pair is preferably a mirror image of the other. Implant 1000preferably has a leading end for placement toward the anterior aspect ofthe vertebral bodies that is configured to conform to at least a portionof the anterior aspect of the vertebral bodies. The upper and lowermembers are preferably articulated at the trailing end of implant 1000.An expander 1022 located proximate the leading end of implant 1000 isused to angulate the upper and lower members of implant 1000 to placethe adjacent vertebral bodies in proper lordosis. Expander 1022 ismanipulated by a tool inserted from a posterior approach through thetrailing end of the implant. For insertion from an anterior approach tothe spine, it is appreciated that in an alternative embodiment, expander1022 may be located proximate the trailing end of the implant with theupper and lower members being articulated at the leading end of theimplant.

The expandable push-in spinal fusion implant may include, be made of,treated, coated, filled, in combination with, or have a hollow forcontaining artificial or naturally occurring materials suitable forimplantation in the human spine. These materials include any source ofosteogenesis, bone growth promoting materials, bone derived substances,bone morphogenetic proteins, hydroxyapatite, genes coding for theproduction of bone, and bone including, but not limited to, corticalbone. The implant can also be formed of material such as metalincluding, but not limited to, titanium and its alloys or ASTM material,surgical grade plastics, plastic composites, ceramics, or othermaterials suitable for use as a push-in spinal fusion implant.

The implant can include in part of materials that are bioabsorbable inthe body. The push-in implant of the present invention can be formed ofa porous material.

The present invention is directed to expandable push-in implants onlynot including push-in implants having substantially arcuate upper andlower members oriented toward the adjacent vertebral bodies and designedto engage the vertebral bodies only along arcuate cuts therein typicallyformed by a drill. Further, the present invention is not directed tothreaded implants requiring rotation for insertion into the implantationspace in the spine. The implant of the present invention does not have acircular cross-section along a substantial portion of its length.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them, is that theexpandable push-in spinal fusion implant adapted for linear insertionacross disc space D between two adjacent vertebral bodies V of a humanspine has an upper member having an upper surface adapted for placementtoward and in contact with the upper of the adjacent vertebral bodies V.The implant also has a lower member having a lower surface adapted forplacement toward and in contact with the lower of the adjacent vertebralbodies V. The upper and lower surfaces of the upper and lower membershave at least one opening. The openings of the upper and lower surfacesare in communication with one another to permit for the growth of bonefrom vertebral body V to adjacent vertebral body V through the implant.Preferably, on the exterior of each of the opposed upper and lowersurfaces of the upper and lower members is at least a portion of abone-engaging projection adapted for linear insertion. A blocker in theform of an expander preferably is located proximate at least one of theends to hold at least a portion of the upper and lower members apartfrom one another to increase the implant height.

There is disclosed in the above description and the drawings implants,which fully and effectively accomplish the objectives of this invention.However, it will be apparent that variations and modifications of thedisclosed embodiments may be made without departing from the principlesof the invention or the scope of the appended claims.

1. A push-in orthopedic implant for linear insertion at least in partbetween two adjacent bone masses, said implant comprising: an uppermember having an upper surface adapted for placement toward and intocontact with one of the adjacent bone masses, said upper surface beingnon-arcuate along a substantial portion of the length of said implant,said upper surface having at least one opening adapted to communicatewith one of the adjacent bone masses, said upper member having aproximal end and a distal end, and said upper member including a firsttrack portion positioned adjacent one of said proximal and distal endsof said upper member; a lower member having a lower surface adapted forplacement toward and into contact with the other of the adjacent bonemasses, said lower surface being non-arcuate along a substantial portionof the length of said implant, said lower surface having at least oneopening adapted to communicate with the other of the adjacent bonemasses, said openings of said upper and lower surfaces being incommunication with one another and adapted for permitting for the growthof bone from adjacent bone mass to adjacent bone mass through saidimplant, said lower member having a proximal end and a distal endcorresponding to said proximal end and said distal end of said uppermember, respectively, and said lower member including a second trackportion positioned adjacent one of said proximal and distal ends of saidlower member, the position of said second track portion corresponding tothe position of said first track portion, said upper and lower memberscontacting and articulating therebetween adjacent one of said proximalends and said distal ends of said upper and lower members and allowingfor expansion of the height of said implant, said upper and lowermembers having a first position relative to one another allowing for acollapsed implant height and a second position relative to one anotherallowing for an increased height, and said upper and lower membersadapted to interlock with one another to stop said upper and lowermembers from being moved apart from one another more than apredetermined distance; at least one blocker provided in said first andsecond track portions and positioned adjacent said one of said proximaland distal ends of said upper and lower members, said blocker adapted tocooperatively engage and hold at least a portion of said upper and lowermembers apart so as to maintain the increased height of said implant andresist the collapse of said implant to the collapsed implant height whensaid implant is in a final deployed position, said blocker beingconfigured to rotate partially within said first and second trackportions about an axis generally parallel to a longitudinal axis of saidimplant and to remain in a plane generally perpendicular to thelongitudinal axis while transitioning said upper and lower members fromsaid first position to said second position, said first and second trackportions adapted to restrain movement of said blocker along the lengthof said implant; and a hollow defined between said upper and lowermembers from adjacent said proximal end to adjacent said distal end incommunication with said openings in each of said upper and lowersurfaces, said hollow being adapted to receive fusion-promotingsubstances, and said hollow being unobstructed by said blocker.
 2. Thepush-in implant of claim 1, wherein said implant has a constant width inboth the first position and the second position.
 3. The push-in implantof claim 1, wherein said implant has side walls and said blocker doesnot contact said side walls when said implant is in the final deployedposition.
 4. The push-in implant of claim 1, wherein said blocker movessaid upper and lower surfaces of said upper and lower members from oneof a parallel orientation and an angled orientation relative to oneanother in the first position to an angled orientation relative to oneanother in the second position.
 5. The push-in implant of claim 1,wherein said blocker has an upper surface, a lower surface, and sidesurfaces as defined when said blocker is positioned to increase theheight of said implant, said side surfaces intersecting said upper andsaid lower surfaces at two pairs of diametrically opposed junctions. 6.The push-in implant of claim 5, wherein said two pairs of diametricallyopposed junctions are a pair of diametrically opposed corners and a pairof diametrically opposed arcs.
 7. The push-in implant of claim 6,wherein said two diametrically opposed arcs are each of the same radius.8. The push-in implant of claim 7, wherein the distance across said twodiametrically opposed arcs generally approximates the distance betweensaid upper and lower surfaces of said blocker.
 9. The push-in implant ofclaim 1, wherein said upper and lower members have a rotationalarticulation therebetween adjacent one of said proximal end and saiddistal end of said upper and lower members.
 10. The push-in implant ofclaim 1, wherein said implant has an interior, at least one of saidupper and lower surfaces has a screw hole passing therethrough adaptedto receive a screw passing from said interior of said implant into oneof the adjacent bone masses.
 11. The push-in implant of claim 1, furthercomprising at least a portion of a bone-engaging projection adapted forlinear insertion formed on the exterior of each of said upper and lowersurfaces for penetrably engaging the adjacent bone masses.
 12. Thepush-in implant of claim 11, wherein said bone-engaging projection isselected from one of a ratchet, a surface roughening, and a knurling.13. The push-in implant of claim 1, in combination with a bone growthpromoting material.
 14. The push-in implant of claim 13, wherein saidbone growth promoting material is selected from one of bonemorphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 15. The push-in implant of claim 1, wherein saiddistal ends of said upper and lower members are symmetrical from side toside.
 16. The push-in implant of claim 1, wherein said distal ends ofsaid upper and lower members are asymmetrical from side to side.
 17. Apush-in orthopedic implant for linear insertion at least in part betweentwo adjacent bone masses, said implant comprising: an upper memberhaving an upper surface adapted for placement toward and into contactwith one of the adjacent bone masses, said upper surface beingnon-arcuate along a substantial portion of the length of said implant,said upper surface having at least one opening adapted to communicatewith one of the adjacent bone masses, said upper member having aproximal end and a distal end, and said upper member including a firsttrack portion positioned adjacent one of said proximal and distal endsof said upper member; a lower member having a lower surface adapted forplacement toward and into contact with the other of the adjacent bonemasses, said lower surface being non-arcuate along a substantial portionof the length of said implant, said lower surface having at least oneopening adapted to communicate with the other of the adjacent bonemasses, said openings of said upper and lower surfaces being incommunication with one another and adapted for permitting for the growthof bone from adjacent bone mass to adjacent bone mass through saidimplant, said lower member having a proximal end and a distal endcorresponding to said proximal end and said distal end of said uppermember, respectively, and said lower member including a second trackportion positioned adjacent one of said proximal and distal ends of saidlower member, the position of said second track portion corresponding tothe position of said first track portion, said upper and lower membersarticulating therebetween adjacent one of said proximal ends and saiddistal ends of said upper and lower members and allowing for expansionof the height of said implant, said upper and lower members having afirst position relative to one another allowing for a collapsed implantheight and a second position relative to one another allowing for anincreased height, and said upper and lower members adapted to interlockwith one another to stop said upper and lower members from being movedapart from one another more than a predetermined distance; at least oneexpander positioned in said first and second track portions, said firstand second track portions adapted to restrain movement of said expanderalong the length of said implant, said expander adapted to expand saidupper and lower members from the first position to the second positionwhen moved from an expander insertion position to a final deployedexpander position, said expander being adapted to cooperatively engageand hold at least a portion of said upper and lower members apart so asto maintain the increased height of said implant and resist the collapseof said implant to the collapsed implant height when said implant is ina final deployed position, said expander having a depth, a first heightcorresponding to the height of said expander when said implant isinitially inserted between the adjacent bone masses, and a second heightcorresponding to the height of said expander when said expander isrotated into a final deployed position to increase the height of saidimplant, said second height of said expander being greater than saidfirst height of said expander, said first height and said second heighthaving an approximately perpendicular relationship, said first heightand said second height each being greater than said depth; and a hollowdefined between said upper and lower members from adjacent said proximalend to adjacent said distal end in communication with said openings ineach of said upper and lower surfaces, said hollow being adapted toreceive fusion-promoting substances, and said hollow being unobstructedby said blocker.
 18. The push-in implant of claim 17, wherein saidimplant has a constant width in both the first position and the secondposition.
 19. The push-in implant of claim 17, wherein said implant hasside walls and said expander does not contact said side walls when saidimplant is in the final deployed position.
 20. The push-in implant ofclaim 17, wherein said expander moves said upper and lower surfaces ofsaid upper and lower members from one of a parallel orientation and anangled orientation relative to one another in the first position to anangled orientation relative to one another in the second position. 21.The push-in implant of claim 17, wherein said expander has an uppersurface, a lower surface, and side surfaces as defined when saidexpander is positioned to increase the height of said implant, said sidesurfaces intersecting said upper and said lower surfaces at two pairs ofdiametrically opposed junctions.
 22. The push-in implant of claim 21,wherein said two pairs of diametrically opposed junctions are a pair ofdiametrically opposed corners and a pair of diametrically opposed arcs.23. The push-in implant of claim 22, wherein said two diametricallyopposed arcs are each of the same radius.
 24. The push-in implant ofclaim 23, wherein the distance across said two diametrically opposedarcs generally approximates the distance between said upper and lowersurfaces of said expander.
 25. The push-in implant of claim 17, whereinsaid upper and lower members have a rotational articulation therebetweenadjacent one of said proximal end and said distal end of said upper andlower members.
 26. The push-in implant of claim 17, wherein said implanthas an interior, at least one of said upper and lower surfaces has ascrew hole passing therethrough adapted to receive a screw passing fromsaid interior of said implant into one of the adjacent bone masses. 27.The push-in implant of claim 17, further comprising at least a portionof a bone-engaging projection adapted for linear insertion formed on theexterior of each of said upper and lower surfaces for penetrablyengaging the adjacent bone masses.
 28. The push-in implant of claim 27,wherein said bone-engaging projection is selected from one of a ratchet,a surface roughening, and a knurling.
 29. The push-in implant of claim17, in combination with a bone growth promoting material.
 30. Thepush-in implant of claim 29, wherein said bone growth promoting materialis selected from one of bone morphogenetic protein, hydroxyapatite, andgenes coding for the production of bone.
 31. The push-in implant ofclaim 17, wherein said distal ends of said upper and lower members aresymmetrical from side to side.
 32. The push-in implant of claim 17,wherein said distal ends of said upper and lower members areasymmetrical from side to side.